Hood design-Week 2
OBJECTIVE: Design the Hood outer panel, inner panel, and the necessary reinforcements by following the Master section mentioned with the design parameter explained in the videos. Submit an assembly of Hood inner panel, outer panel, latch, hinge, and reinforcements.
Introduction
The hood or bonnet is the hinged cover over the engine of motor vehicles. Hoods can open to allow access to the engine compartment for maintenance and repair. On front-mounted cars, the hood may be hinged at either the front or the rear edge, or in earlier models it may be split into two sections. A further variant combines the bonnet and wheel arches into one section and allows the entire front bodywork to tilt forwards around a pivot near the front of the vehicle. From a design perspective, the hood should meet some specific conditions like pedestrian safety, a hood head zone for the lock striker, force distribution when subjected to frontal collision, manufacturability, etc.
A typical hood assembly consists of a hood outer panel, latch & striker, hinge, and hood stay.
The Hood is made out of the same material as the rest of the bodywork, which is steel and aluminum.
Deep drawing, hemming, blanking, and piercing are the common sheet metal operations that are used in manufacturing hoods in automotive industries.
Hood Design Parameters
Hood Thickness Information
Outer Panel Thickness: 0.75mm
Inner Panel Thickness: 0.75mm
Reinforcement Thickness: 1.5mm
Master Section
COMPONENTS:
Hood Outer Panel
The outer panel is the aesthetic element of a car. It is the styling team that provides the skin for the outer panel. The shape, position, and size of the hood should satisfy the safety norms. The outer panel is attached to the inner panel by hemming. So it is necessary to provide hemming flange and reliefs for the hemming operation.
Hood Inner Panel
The inner panel is the part that gives strength and rigidity to the outer panel. The master section represents the initial
emboss shape and size. It is where the hood balancer and hinges are attached.
Hinge
A hinge is a component that fixes the hood to the engine compartment of the car. One part of the hinge is connected to the engine compartment and the other part is connected to the hood inner panel. The hinge allows the hood to rotate around a fixed axis for opening and closing movement.
Striker
A latch and striker mechanism is provided to lock the hood, the latch and striker ensure that your hood is securely connected to the vehicle and it does not open unexpectedly while driving. The latch is present on the engine compartment while the striker is attached to the inner part of the hood. When tension is applied to the cable from the hood release handle, it pivots the secondary latch, which pulls away from a retaining seat located under the hood. By design, the secondary latch then releases the hood a few inches before a safety latch takes over.
Reinforcement
Reinforcements are provided according to the design requirements. Mainly it is provided at the hinge and latch regions to improve the strength locally. Usually, the thickness of reinforcements will be higher than that of the inner panels and the value varies according to cost and requirement. According to the design requirement here, it is given 1.5mm thickness to both hinge and latch reinforcements.
LATCH TRAJECTORY
Latch trajectory is given by the circle drawn from the hinge axis point. The hinge axis point is the center point of the hinge axis. First, we can fix either the latch or the hinge. If we have fixed the hinge position then we should plot the Trajectory circle for the latch. For proper mating conditions, the striker axis through the tip of the striker should be tangential to the latch trajectory.
MASTIC DATA:
Hood commonly possesses a large surface area and hemming can only be provided through its boundary. We cannot use other joining techniques like welding, riveting, etc because they leave marks on the outer panel which spoils its aesthetic appearance. So, mastic sealants are used to stick the inner surfaces of the outer panel and inner panel. Mastic sealants are elastic compounds that behave like rubber. It is applied between the inner and outer panels at specified spots. Each spot of mastic sealants has its effect around a circular region of 80mm diameter. Thus, the mastic points are arranged in such a way that it covers the areas away from the hemming which is more vulnerable to vibrate.
IMPACT FORCE DISTRIBUTION
A hood design must be made in such a way that when a force is impacted in the front of the hood, all the forces must be directed outwards from the vehicle. It will drastically reduce the impact on the passengers. Here in the figure embosses are designed in such a way that the force is directed to either side of the car.
SHEETMETAL OPERATIONS USED IN HOOD MANUFACTURING PROCESS
Deep Drawing
It is a sheet metal forming process in which a sheet metal blank is radially drawn into a forming die by the mechanical action of a punch. The process is considered deep drawing when the depth of the drawn part exceeds its diameter.
Hemming
Hemming is a forming operation in which the edges of the sheet are folded over other parts or simply folded in order to achieve a tight fit. In-car part production, hemming is used in assembly as a secondary operation after deep drawing, trimming, and flanging operations to join two sheet metal parts (outer and inner) together.
Embossing
Sheet metal embossing is a stamping process for producing raised or sunken designs or relief in sheet metal. This process is carried out by means of matched male and female roller dies, or bypassing the sheet or rolls of metal between rolls of the desired pattern.
Piercing & Blanking
It is a shearing process in which raw sheet metal is pierced with a machining tool, resulting in the creation of a particular shape hole in the sheet. The major difference between blanking and piercing is that in blanking the cut out is the workpiece and the outer part is scrap, while in piercing, the cut out is scrap and the outer sheet is the workpiece.